Regeneration stabilization circuit



-Oct. 17,1944. RANKIN 2,360,794

REGENERATION STABILIZATION CIRCUIT Filed March 12, 1942 I r A ere, g Fig ,1, L fiefizza M INVENTOR 'Ai'roRNEY Patented Oct. 17, 1944 UNITED REGENERATION STABILIZATION CIRCUIT John a. Rankin, Port Washington, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application March-12, 1942, Serial No. 434,311

14 Claims.

My present invention relates to regenerative signal transmission circuits, and more particularly to a novel and improved method and means for stabilizing regeneration.

One of the main objects of my present invention'is to provide in a signal transmission system employing a regenerative circuit, a regeneration stabilizer network which automatically functions to increase the damping of the regenerative circuit upon increase of regeneration above a predetermined and desired magnitude.

Another important object of my invention is to provide in conjunction with a plurality of,

cascaded resonant circuits, all tuned to a common signal frequency, a means for regenerating the last of the circuits, and additional means which is responsive to an undesired increase of regeneration for automatically damping the regenerated resonant circuit.

Still another important object of my invention is to provide in combination with a regenerative signal amplifier, a regeneration stabilizer circuit which includes an electron discharge device whose input and output electrodes are connected between a prior point of the amplifier system and the regenerative circuit respectively,

the stabilizer device normally being non-conductive, and the stabilizer deviceprovidinga flow of damping current for the regenerative input cirtiuit upon an undesired increase of regenera- Still other objects of my invention are to improve generallythe simplicity and emciency of regenerative high frequency circuits, and more particularly tov provide a stabilizer network for regenerative amplifier circuits'which is not only reliable and efficient in operation, but is economically manufactured and assembled.

.The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims; the invention men, however, as to-both its organization and method of operation will best be understood by reference to the following description taken ing, wherein like reference characters in the different figures designate similar circuit elements, there is shown in Fig. 1 a pair of cascaded high frequency amplifier tubes. Amplifier tube I has its control grid 2 connected to the high potential side of a tuned input circuit 3. The latter may be coupled to'the tuned circuit ,4. Assuming that the amplifier l is in the intermediate frequency (I.-F.) network of a superheterodyne receiver, then the circuits 4-3 would each be tuned to the operating I. F. value. The latter may be chosen to be 455 kilocycles (kc.) if the receiver is adapted to operate in the broadcast range of 550, to 1700 kc. The usual signal wave collector, converter and subsequent I. F. stages may precede the circuit 4. Of course. the invention is equally applicable to other frequency ranges, either below 550 kc. or above 1'700,kc. Furthermore, the amplifiers may be in a wave transmission system other than a receiver. In-

deed, the invention is applicable to any system I amplifier tube 1 to ground. The input circuit 8 is connected between the grid Ill and ground. The plate II has the tuned output circuit 9 connected thereto. The tuned circuit 9' may feed the amplified high frequency energy to any desired type of utilization network.

' The circuits 4I-8--l--98' are each tuned to the operating input frequency; in the assumed example this would be the I. F. value.

Regeneration in amplifier I is provided by capacity ll between the plate ii and grid 1. The

capacity I 3 may be an actual physical condenser outside the tube, or it may even be provided by the inherent capacity within the tube between grid I I and plate] I.

An example of a stabilizing means, in accord- I ance with my present invention, is shown in Fig. 1. The tube 14 has its grid ll coupled by condenser li to apoint on the coil 3' of the input circuit 3 of tube l. The tap Il may be provided so as to adjust the point on coil 3' to which the grid II is to be connected. The cathode of tube grid I is represented by the wave AiB1-Ci,

I4 is grounded; while theplate I1 is connected by an adjustable tap to coil 6' of output circuit 6 of tube 2. The grid 15 of stabilizer tube l4 may be biased negatively through resistor l4 from any negative voltage source. It will be seen that the plates of tubes 54 and l are provided with positive potential through the common coil To explain the operation of the invention, there will first be considered the regenerative action taking place in the stage including tube 1. In that stage, as condenser I3 is increased in value of capacity from zero there occurs an increased reflection of negative resistance between grid Ill and cathode 12. This raises the Q of the input circuit 8. Even though the circuit 8 be made to oscillate by virtue of the increased value of capacity l3, there will be no relative change cults will increase. That is, the ratio of the output voltage across circuit 9 to the voltage across circuit 3 will increase as C13 increases.

This means that the negative resistance, due to regeneration, between grid In and cathode 12 has increasedtheQ of input circuit 8, and that the gain of the coupled tuned circuits 88 is increased. Likewise, the gain irom grid 2 to either of circuits 6 or 8 will be increased.

. The tube It and its associated circuits is ro vided' to maintain the gain between any two points of the amplifier system constant. This is done by introducing damping when the gain between the said two points increases above a predetermined value. "The two points in Fig. 1 are,-

the points where the taps l6 and H are set. The points are designated as A and B respectively. The manner in which the stabilizing circuit acts to stabilize the regenerative,process will now be explained, special reference being made to Figs. 4a, 4b and 4c.

Assume that the regenerative tube I has been adjusted to provide regeneration of a predetermined magnitude by virtue of the proper adjustment of condenser II. The gridli of the stabilizing tube I4 is connected to a suitable point A on coil 3'; The grid I! is biased negatively to an extent such as to be sufllcient to produce plate current cut-oil or tube It. The tube ll may be a triode of a given mu. 'The points'A and B are so chosen that the gain between these two points is mu. The Eg-Ep characteristic of the stabilizer tube I4 is shown in Fig. 4a. The line L is drawn with a slope of mu.

Considering, now, Fig. 4b, a value cra -Es is selected. This is the exact value ot-the plate operating voltage of tubes I and Id. The bias for the control grid 2 is then fixed by this value or Es and will be equal to a value or Ec- Tliis' value of En is sufficient to exactly produce plate current cut-oi! and is equal to Eb/mu. As signal energy is applied to the input circuit the grid I5 of tube ll will have applied to it from input circuit 3 a given amount or input signal. Similarly a signal will be applied to the plate I! from the output circuit 8 of tube i. The grid voltage at and plate 0! tube M is slightly higher than mu.

" the mu 0! the tube.

phase as shown. As long as the high frequency voltage applied to the grid 15 and plate ll of tube H remain in the ratio of mu, then no plate current will flow in'tube l4. This will be understood by following the two waves from A to B to C, and noting that the projection of each wave at each point intersects the line L.

Referring, now, to Fig. 4c, the condition is represented in which the gain between selected points A and B 'has increased above that for stability, and this increase is due to an increase in regeneration or some factor that affects the regenerator tube. In this-diagram the plate voltage is greater by mu times the grid voltage applied to tube M. 'If we now follow the wave through its various points, it will be seen that at point A; no plate-current flows due to the fact that the projections of the grid voltage wave and the projections of the plate wave intersect on line L which has a slope equal to mu. At "point Bl the projections intersect at point B; which is below the line L. In this region the tube I4 is beyond plate current cut-off, and, hence, plate current cannot flow. However, the projection of point C1 of the grid voltage wave and point C: of the plate voltage wave intersect at point C: which is above the line L. Hence, plate current will flow in tube ll. The late current will flow over the half cycle in which, the plate voltage is positive. The fact that plate current flows will damp the circuit across which the plate is connected, and tend to lower its impedance and hence counteract the increased regeneration.

In the circuit shown in Fig. 1, the circuit 6 will also be dampeddr the gain between the grid and plate or tube ll should fall below eration, thegrld l8 hculd be connected to a point such that the gain between the grid and The tube 14 adds a capacity between the grid and plate of tube I that would have to be neutralized tor satisfactory operation. Tube l is normally biased, and the bias is fixed. It is only tube ll which is biased to cut-oi! as long as regeneration of tube 1 is below the predetermined "magnitude. The stabilizer tube it has its grid and plate alternating voltages so chosen as to be in balance thereby to prevent plate current now.

When the-plate current or tube It flows, the damping o! circuit -I will in turnaflect the damping of circuit 8.

In Fig. .2 there is shown a simplified form of the invention possessingicertaln advantages. In. place or the triode stabilizer tube It there is .utilized a diode 20. The cathode 2| of the lating signal frequency, is positioned between circuits 8 and 8. In other words,the three circuits 8, 30 and 8 are each tuned to the same transmitted frequency; circuits 8 and 3e are magnetically coupled at M, and circuits Q0 and 8 are magnetically coupled as at Mr. It will, theretom, be seen that points A and B in Fig. 2 are located respectively at the output circuit of amplifier I and the input circuit or the regenerative amplifier. Hence, it will be seen that the ence, for satisiactory op-.

- departing from the scope of my invention, as

invention is not limited to providing the stabilizing circuit between the input-and output circuits of the-amplifier preceding the regenerative amplifier, but thatthe stabilizing circuit maybe provided between the coupled tuned circuits between amplifier tubes I and I.

The diode 20 is connected across the input and output circuits of a transformer network 8-30-8. The transformer is so arranged that points A and B are in phase, and the gain be-' greater than, unity with the-desired amount of regeneration effective in tube If the regem eration at tube I increases for any cause, the gain between points A and B will likewise increase, but the diode will then draw current anddamp the input circuit 8 of the regenerative amplifier thereby to prevent the gain from rising. This results in stabilization of the regenerative amplifier.

The diode 20 may be replaced by a. low mu triode of the type shown at H of Fig. 1'. In this case the circuit would have to be arranged so that points A and B are out of phase and separated by a gain of mu, or slightly more than mu. The circuit shown in Fig. 3 is similar to that shown in Fig. 2 with the exception that the tube 14 of Fig. 1 replaces the ,diode 20. This circult is preferred and has the advantage over that shown in Fig. 1 in that only passive circuit elements appear between the two points A and B at which the stabilizing tube is connected. As shown in Fig. 3 the condenser l6 couples the grid i to-point A. The cut-off bias is applied to grid i5, and the plate I1 is connected to a source of positive potential through the radio frequency choke coil 60. The point B of circuit 8 is connected to the plate Il by thedirect current blocking condenser 50. The points A and B in Fig. 3 are arranged to be 180 degrees out of phase. These points have a voltage difference of .mu times, or slightly greater than mu. In this case the tube I will damp circuit 8 if the gain between points A and 3 increases due to any increase in regeneration.

It will now be seen that I have provided various regeneration stabilizing circuits which have in common certain generic structures and functions. From a generic viewpoint, an amplifier system embodying a regenerative amplifier '10 tween points A and B is equal to, or slightly set forth in the appended claims.

What I claim is: 1. In a wave transmissionsystem of the type comprising a resonant wave input circuit and a cuit and said succeeding regenerative circuit,

applying wave voltage to the input and output points of said path, and introducing damping into said regenerated resonant circuit from said path by virtue of said path becoming conductive for direct current in response to an increase in regeneration of said succeeding circuit above said predetermined point.

2. In combination with a high frequency amplifier tube having regenerative coupling between its output and input electrodes, a res-' onant circuit coupled between the input electrodes of said amplifier tube, a wave input circuit .preceding said amplifier input circuit and separated therefrom by at least one intervening resonant circuit, means forpreventing an increase in regeneration of said amplifier above a predetermined magnitude, said means comprising an electron discharge device having an input electrode coupled to a point on said wave input circuit and an output electrode coupled to a point on said amplifier input circuit, means for normally rendering said electron discharge device non-conductive, and said device becoming conductive and permitting electron currents to flow through said amplifier input circuit in response to an increase in regeneration above said predetermined magnitude.

3. A regenerative signal amplifier tube provided with a resonant input circuit tuned to a desired signal frequency, a second resonant circuit preceding said input circuit, at least one resonant circuit located between said amplifier input circuit and said second resonant circuit,

the three resonant circuits each being tuned to the desired signal frequency, a regeneration stabilizing circuit comprising an electron discharge device provided with an input electrode and an output electrode, a signal coupling connection between the input electrode of said dee vice and said second resonant circuit, a signal generative amplifier produces a predetermined amount of regeneration. However, upon an increase in regeneration the aforesaid electron discharge tube becomes conductive, and permits current to fiow through the regenerative amplifier input circuit thereby increasing its damping to an extent suiilcient to counteract the unde sired increase in regeneration. The electron dis* charge device may be of any desired type, and the input and output electrodes thereof have high frequency voltage applied thereto from the .aforementioned spaced points.v

While I have indicated and described several coupling connection between said amplifier input circuit and the output electrode of said device,. and means normally preventing electron current to flow in' said stabilizer device in the absence of regenerative action in said regenzraltive amplifier above a predetermined magni- 4. A regenerative signal amplifier tube provided with a resonant input circuit tuned to a desired signal frequency, a second resonant'circuit preceding said input circuit, at least one resonant circuit located between said amplifier input circuit and said second resonant circuit, the three resonant circuits each being tuned to the desired signal frequency, a regeneration stabilizing circuit comprising an electron discharge device provided with an input electrode and an output electrode, a signal coupling connection between the input electrode of said device and said second resonant circuit, a signal coupling connection between said amplifier input circuit and the output electrode of said device, mean's normally preventing electron current to flow in cuit preceding said input circuit, at least one resonant circuit located between said amplifier input circuit and said second resonant circuit, the three resonant circuits each being tuned to the desired signal frequency, a regeneration stabilizing circuit comprising an electron discharge device provided with an input electrode and an Output electrode, a signal coupling connection between the input electrode of said device and said second resonant circuit, a signal coupling connection between saidiamplifier input circuit and the output electrode of said device, means normally preventing electron current to flow in said stabilizer device in the absence of regenerative action in said regenerative Y amplifier above a predetermined magnitude, said electron discharge device being a diode, and said intervening resonant circuit being reactively coupled to each of said amplifier input-circuit and said second resonant circuit.

6. Aregenerative' signal amplifier tube provided with a resonant input circuit tuned to a desired signal frequency, a second resonant circuit preceding said input circuit, at least one resonant circuit located, between said amplifier input circuit and said second. resonant circuit, the three resonant circuits each being tuned to the desired signal frequency, a regeneration stabilizing circuit comprising an electron discharge device provided with an input electrode and an output electrode, a signal coupling connection between the input electrode of said device and said second resonant circuit, a signal coupling connectionbetween said amplifler input circuit and the output electrode of said device, means normally preventing electron current to flow in said stabilizer device in the absence of regenera tive action in said regenerative amplifier above a predetermined magnitude, a second electron discharge device connected in coupling relatioii between said second resonant circuit and said cascaded resonant circuit which precedes the last resonant circuit by one resonant circuit, and means for biasing said input electrode for preventing electron current flow to the output electrode of said tube.

9. In a wave transmission system 01' the type comprising a resonant wave input circuit and a succeeding resonant circuit, the method which includes tuning both resonant circuits to a common wave frequency, establishing the succeeding circuit to a predetermined degree of regeneration, providing a normally non-conductive direct current path between said input circuit and said succeeding circuit, applying wave voltage to the input and output of said path, and damping said regenerated resonant circuit from said path. by virtue of said path becoming conductive for direct current in response to an increase in regeneration of said succeeding circuit above said pre-' ing said input electrode to one of the cascaded resonant circuit which precedes the last resonant device non-conductive thereby preventing direct intervening resonant circuit, and said amplifier input circuit being reactively coupled to said intervening circuit.

7. In combination with a plurality of cascaded resonant circuits each tuned to a common signal circuit, and means for normally rendering said current-flow to the output electrode of said electron discharge device. i

11. In a wave transmission system of the type comprising a resonant wave inputcircuit and a succeeding resonant circuit, the method which includes-tuning the resonant circuits to a common wave frequency, decreasing the resistance of the succeeding circuit to a predetermined low value,establishing a normally non-conductive direct current path between said input circuit and said succeeding circuit, applying wave voltage to the input and output points, of said path, and

introducing. resistance into said succeeding resonant circuitfrom said path by virtue of said path becoming conductive and passing direct current in response to a decrease in resistance of said succeeding circuit below said predetermined low value.

. 12. In combination with a wave amplifier tube having regenerative coupling between its output'and input electrodes, a resonant input circuit coupled between the input electrodes of said amplifler tube, a wave input circuit preceding said amplifier input circuit, an electron discharge device having an input electrode coupled to a point wave frequency, means for regenerating the last L of the cascaded resonant circuits, an electron j,

discharge device having input and output elec-" tr0des,'means connecting the output electrode of said'device to said last resonant circuit, additional means for connecting said input'electrode to one of the cascaded resonant circuit which wave frequency, means for regenerating the last of the cascaded resonant circuita-a'tube having,

an input electrode and an output electrode, means connecting the output electrode oi said tube to said last resonant circuit, additional means for connecting said input electrode to one .0! the on said wave input circuit and an output electrode coupled to a point on said amplifier input circuit, said electron discharge device being normally'non-conductive, and said device becoming conductive and permitting electron currents to flow through said amplifier input circuit in response to an increase in regeneration above a predetermined magnitude.

13; In combination with a plurality of casceded wave transmission circuits, means for regenerating the last 01 the cascaded circuits. an electron discharge device having an input electrode and an output electrode, means connecting the output electrode of said device to said last circuit, additional means for connecting said input electrode to one of the cascaded circuits which precedes the last circuit by at least one intervening circuit, and means preventing electron current flow to the output electrode of said electron discharge device in the absence 0! regeneration at said last circuit being above a. predetermined magnitude.

14. In a wave transmission system of the type comprising a resonant wave input circuit and a succeeding resonant circuit, the method which includes transmitting wave energy or a predetermined frequency through said circuits, establishing the succeeding circuit at a predetermined degree of regenerationmroviding a normally mm 10 

